If you notice that on your Xiaomi smartphone, the brightness of the screen changes for no apparent reason — it dims indoors abruptly, it suddenly becomes brighter outside — it's not always a defect. Most often, this behavior is due to the work of built-in functions or system settings, but sometimes the reasons go deeper, from sensor failure to software errors.
In this article, we'll look at all the possible reasons why screen brightness changes on Xiaomi by itself, from the banal to the rare, how to check adaptive lighting, calibrate sensors, reset to factory settings, and even diagnose hardware malfunctions, and at the end, an FAQ that answers frequent user questions.
1. Adaptive brightness: how it works and why it fails
The main reason for the spontaneous brightness change on Xiaomi is the Adaptive Brightness function, which automatically adjusts the brightness of the screen depending on the light around it using data from the light sensor (located next to the front camera), which is convenient in theory, but often irritating in practice.
Adaptive brightness problems arise from:
- 🔄 Incorrect calibration of the sensor – the smartphone “thinks” that the surroundings are darker or lighter than they really are.
- 📱 Sensor contamination – dust, film or cover block light, distorting readings.
- 🤖 Failures in MIUI — After updating the firmware, the adjustment algorithm may not work stable.
- 🔋 Charge savings – in battery mode, the function becomes more aggressive, sharply reducing brightness.
To check if the adaptive lighting is to blame, turn it off:
- Go to Settings → Display → Brightness.
- Turn off Adaptive Brightness (or Auto Brightness in older versions of MIUI).
- Manually set a comfortable brightness level and observe the behavior of the screen for 10-15 minutes.
If the brightness stopped jumping after the function was turned off, the problem was solved. If not, read on.
2. Illumination sensor: diagnostics and cleaning
The light sensor is a small sensor next to the front camera that measures the level of light. If it is contaminated or damaged, the smartphone gets the wrong data and adjusts the brightness incorrectly. On the Xiaomi Redmi Note 10/11, POCO X3/X4 and other models, the sensor is often closed with a protective mesh, which eventually gets clogged with dust.
How to check the sensor:
- Turn on adaptive brightness (Settings → Display → Brightness).
- Close the sensor with your finger – the screen should dim (simulation of darkness).
- Direct the light of the flashlight to the sensor - the brightness should increase.
If the reaction is not adequate (for example, when the sensor is closed, the screen becomes brighter), the problem is:
- 🧹 Pollution – wipe the sensor with a soft napkin dipped in alcohol (without pressing!).
- 🛠️ Damage – if the sensor is not responding at all, the plume may have gone away or the sensor may have failed.
- 📱 Film/coverage – some protective glasses and covers block infrared light, interfering with the sensor.
💡
On Xiaomi 12/13 models, the light sensor is hidden under the display. To clean it, use a dry cotton swab with minimal effort.
If cleaning doesn’t help, try recalibrating the sensor:
- Open the Settings. → The phone.
- Tap 5-7 times on the MIUI version to activate Developer Mode.
- Back to Settings → Additionally. → For developers.
- Find the option to Turn off automatic brightness (if any) or Reset adaptive brightness.
3. MIUI failures: updates, cache and reset
Software errors are the second most common cause of unstable brightness, especially after updating MIUI or installing custom firmware, the system may not process sensor data correctly or conflict with applications that try to control brightness (for example, Twilight, Lux Auto Brightness).
What to do:
- 🔄 Reboot your smartphone – sometimes it resets temporary crashes.
- 🗑️ Clear the system cache: Go to Settings → Annexes → App management. Tap three points (⋮) → Show them system. Find settings and system. UI, clear the cache.
- 📲 Update. MIUI — Check for updates in Settings → The phone. → Updating the system.
- ⚙️ Reset the display settings: Settings → Display. → Additionally. → Resetting display settings